Today I committed the big change: I moved mailing-lists.ent from out of the Handbook directories and into the per-language share/sgml directory, and created a PUBLIC identifier in each language-specific catalog file. Speaking of that, I think I need to move all the 'language-specific' sections of doc/share/sgml/catalog into each language's own catalog.

Also, if this goes well and without fallout, a move of the authors.ent and other such files into share/sgml directories and into PUBLIC identifiers (instead of SYSTEM) is not far behind.

A small detail: Seems like nobody really prepared to have much inside of doc/lang/share/sgml as the validate target, which is used to ensure that large documents such as the Handbook would build without actually building them, did not bother to check the language-specific catalogs whatsoever. So I fixed that, too.